The ascending acidity order of the following H atoms is

Alkynes are acidic because they can release hydrogen atoms to form alkylide ions, because the hydrogen is attached more electronegative $\mathrm{sp}$ hybridised carbon. After that alkenes are more acidc than alkanes due to the presence of ${\mathrm{sp}}^2$ carbon atom in alkenes. Among the two alkanes acidic nature order is decided by the inductive effect. Methyl groups are electron releasing groups, hence they decrease the acidic nature. Hence, the overall order is

Stability of conjugate base $\propto$ acidic strength

$\mathrm{C}<\mathrm{D}<\mathrm{B}<\mathrm{A}$